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| Birds wing to Wavecrest By Lou Sian--[ lou@hmbreview.com ] Published/Last Modified on Wednesday, November 14, 2007 3:49 PM PST Every few years for reasons unknown, Wavecrest becomes a smorgasbord for raptors. And this year seems to be a peak within a peak, says Alvaro Jaramillo, biologist for the San Francisco Bay Bird Observatory. Birdwatchers have spotted hawks and owls in unusually large numbers since September, spurring lively chatter on the Internet and attracting photographers from around the Bay Area. "People have been coming from all over and posting their photos on the Internet," said Jaramillo. "From the blufftop field, you can see voles run around and raptors perch on every house that has white droppings." A vole is California's version of the common house mouse, but its tail is shorter. It's food for birds of prey, foxes, bobcats and coyotes. The hawks have been a photographer's dream, staying close to the sure and plentiful supply of voles. Though overcast and not particularly good for bird-watching, the weedy field west of Railroad Avenue was replete with predator and prey alike during the last week of October. Along the east side of the street, the steeply pitched roofs of houses made excellent perches for the raptors. The stationary hawks were actually hunting Jaramillo said. One day last week, a red-tailed hawk flew at a young Northern harrier rising from the field. The two engaged briefly, circled back and clasped talons, whipping each other away like figure skaters in midair. Jaramillo, who lives on a street that ends at Railroad Avenue, says the harriers and kites have been on the bluffs between Kelly Avenue and Wavecrest Road since July. One day in September, he counted 56 white-tailed kites headed for Wavecrest. He estimated that as many as 100 may have been roosting at Wavecrest. In the evening, Jaramillo counted 15 barn owls. As many as 40 barn owls could have been in the area. These represent record-breaking numbers for the area say experts who have been counting bird populations for decades. Gary Deghi, vice president of the Sequoia Audubon Society, has participated in the annual Christmas Bird Count in San Mateo County for more than 20 years. He lives in nearby Ocean Colony. "This past fall, in September, the white-tailed kites have been roosting en masse," said Deghi. "They're a gregarious species. In the fall and winter they come to communally roost." The last great area of raptor research revolves around how birds communicate a prey outbreak over long distances, said Allen Fish, director of the Golden Gate Raptor Observatory in the Marin Headlands. "It's a big mystery in the area of biology how raptors trade information about where prey outbreaks are occurring from hundreds of miles away," Fish said. "We've tracked raptors into small regions that have outbreaks, and for no reason, they move quickly into the area." Fish can think of a number possible explanations. The San Mateo County coast lies within the migration path, and they may have stumbled onto the blufftop field. But for a species that has evolved for 30 million years, it seems less likely that the birds continued through time by depending on chance encounters. Raptors can see long distances and in greater detail, Fish said. Where people may see a green pine bough, a raptor sees the bugs on the pine needles of the pine bough. Recent studies in Scandinavia and Northern Europe have shown that Eurasian kestrals, another raptor species, can see in the ultraviolet range. The kestrals can track mouse urine in the laboratory and in the field. Although it's hard to say what the image is like to a kestral, it may be that the markings glow and reflect in a field like blacklight traces. Fish recalls seeing a hawk fly over the Marin Headlands, winging its way north. "A raptor flew over within hours after eating," Fish said. "It's crop was full, about the size of a golf ball in its throat. If I can see that, can't the other hawks see that?" • Voles are key to raptor population Voles are mouse-like rodents that are five to eight inches in length. Active day and night and throughout the year, they are found in grasslands across California. The population peaks four to five times annually in fairly local areas rather than over a large range, said Bill Lidicker, curator of mammals at the Museum of Vertebrate Zoology at the University of California, Berkeley. "It's strange and surprising," Lidicker said about the vole irruption in the fields between Kelly Avenue and Wavecrest Road. "They don't usually breed in summer because it's too dry. They could have started breeding in September. They churn out a litter every three weeks." Lidicker says that vole populations are not well adapted to surviving over the summer, but the early rains at the end of summer may account for the large numbers of voles seen in the area this fall. The voles have attracted an unprecedented number of raptors to the area, delighting photographers and birdwatchers alike. - Lou Sian |